Acid leaching of pectinous materials



Patented Apr. 4, 1 950 ACID LEACHING OF PECTINOUS MATERIALS Harry S. Owens, Berkeley, Calif., assignor to the United States of America as represented by the Secretary of Agriculture N Drawing. Application November 13, 1947, Serial No. 785,804

12 Claims. (01. 260'209.5)

(Granted under the act of March 3, 1883 as amended April 30, 1928; 370 O. G. 757) Q 1 This application is made under the act of March 3, 1883, as amended by the act of vApril 30, 1928, and the invention herein described, if patented in any country, may be manufactured and used by or for the Govermnent of the United States of America for governmental purposes throughout the world without the payment to me of any royalty thereon.

This invention relates to pectinous materials and more particularly to methods for isolating low-methoxyl pectinic acids from vegetable materials in which the pectin has been partially demethoxylated in situ; or, stated in other words, from vegetable materials in which the pectin has been de-methoxylated in situ to low-methoxyl pectinic acids (particularly those having a methoxy'content of about 2 to 5%) The process is applicable to vegetable material serving as a natural source of pectin, the pectin of which has been partially de-methoxylated. Such treatment may involve hydrolysis through the use of acid, alkali, or enzymes. Suitable vegetable materials are orange peel, lemon peel, grapefruit peel, apple pomace, pear pomace, carrots, pea hulls, sugar beets,'quinces, grapes, etc.

One prior method for isolating low-methoxyl pectinic acids from vegetable materials in which the pectin had been partially de-methoxylated in situ involved extraction of the material with aqueous sodium hexametaphosphate at a pH'of. about 4.0. The resulting aqueous extract was then treated with alcohol to precipitate the lowmethoxyl pectinic acids.

This method suffers from the disadvantage that it is costly since the sodium hexametaphosphate is a relatively expensive reagent.

It has now been found that the use of sodium hexametaphosphate can be entirely eliminated and the low-methoxyl pectinic acids in the vegetable material rendered water-extractable'by' subjecting the vegetable material to a leaching with an acid in aqueous solution. Thus instead of the afore-mentioned expensive reagent, a relatively cheap acid is used.

I It is an object of this invention to provide IllethOdS for isolating low-methoxyl pectinicacids from vegetable material which has been treated to partially de-methoxylate the pectin in situ.

. Another object of this invention is to provide a method of treating vegetable material, in which the pectin has been partially de-methoxylated' in situ, to render the low-methoxyl pectinic acids easily extractable, said result being attained by leeighing the vegetable material with aqueous ac j extractable,- said result being accomplished A further object of this invention is to provide a method of treating citrus peel, in which the pectin has been partially de-methoxylated in situ, to render the 'loW-methoxyl pectinic acids waterby leaching of the peel with aqueous acid.

Further objects and advantages will be obvious to those skilled in the art from the disclosure herein.

Thepreferred methods of partial y lie-methoxylating the pectin are those disclosed in the patent application of Harry S. Owens and Wil-.

liam D. Maclay, Serial No. 529,016, filed March 31, 1944, now Patent No. 2,444,266,issued June 29, 1948, wherein an aqueous dispersion of citrus peel is subjected to partial de-methoxylation by enzymic hydrolysis, by adding alkali and maintaining a pH of 6 to 10 at a temperature of 0 C. to C. preferably a short period of time of the order of less than about 30 minutes, or with a calculated amount of alkali limited to yield the desired degree of de-methoxylation.

To efiect the ends previously set forth, the

vegetable material, in which the pectin has been partially de-methoxylated in situ, is leached with aqueous acid at a pH from about 0 to about 2.5,

I 50 C. to prevent decomposition of the pectinous Thus a temperature range from substances. about 20 C. to 50 C. is suitable. In many cases it may be necessary to employ several leachings to get the proper results, i. e., the lowering of the calcium content in the vegetable material to about 0.2% or less. The acid leach may be effected by several batchwise treatments with filtration after each treatment. However, the leaching is more readily accomplished by utilizing the countercurrent flow technique disclosed in the application of Robert P. Graham and Allan D. Shepherd, Serial No. 788,076, filed November 25, 1947. To this end the vegetable material may be slowly moved through an extraction zone (a trough equipped with a long screw, for instance) while it is subjected to a countercurrent flow of acid adjusted to the proper pH. In this manner, the acid leach may be accomplished in one operation without the necessity of filtration or unduehandling.

Regardless of what technique is used for the acid leaching, this treatment renders the lowmethoxyl pectinic acids in the vegetable material capable of being extracted with water. After the acid leach is finished, the vegetable material may be immediately subjected to such water extraction or may be dried for future extraction.

In either case the leached (or leached and dried) vegetable material is digested with. water, the pH of the mixture of vegetable material. and water being adjusted to about 3.0 to about 5.0 by the addition of a base such as sodium hydroxide, sodium carbonate, sodium bicarbonate, potassium hydroxide, potassium carbonate, potassium bicarbonate, aqua ammonia, carbonates of ammonia, etc. In this digestion the temperature is preferably raised to boiling (100 C.) although this is not essential. The digestion mixture is. filtered preferably with the addition of a filter aid such as the acid treated diatomaoeous earth filter aids available on the market. The filtrate containing the low-methoxyl pectinic acids in. aqueous solution can be isolated in several ways. According to one. procedure, alcohol is added to the filtrate whereby the low-methoxyl pectinic; acids are precipitated. They are thenseparated. by fi1tration, washed with alcohol and dried, According to another procedure thev low-methoxyl, pectinic acids are precipitated by addition of isopropyl alcohol. Other methods involve spraydry-ingor drum-drying oi theaqueous solution; precipitation of: the low-methoxyl pectinic acids with a soluble aluminumsalt at a pH of? about 4.0, followed by removal of the aluminum from. the. formed aluminumepectinous complex with acidiefled aqueous alcohol; precipitation. with a metal ion. such ascalcium, copper. or nicke1,.fl10wed.by removal of themetal either by washing with acidified aqueous alcohol or by means of; an ion exchange material. A simple but efi'icacious method of isolating low-methoxyl pectinic acids. involves merely adding an acidsuch as sulphuric. hydrochloric, nitric, phosphoric; sulphurous, etc, to thesfiltrateto establish a pH noitexcieeziing: 213, Preferably-not; exceeding 2.0; The low-methox-yk pectinic: acids are-therein; precipitated and: cambe. separated, washed, and dried. The: process of; isolatinglow-methoxyl pectinic acids by. acidkprecipitationis disclosed; and claimed in; the. Patent. application; of Rolland: M1. McCready; Harry: S. Ow.ens',.and.Willia-m.D. Maclay,.Serial. No; 61.6;44'5;,, filed september-ld, 1945, now Patent .No..2,448,8l.-8,. issued September-'7, 1948i The following; examples describe, particulars steps; conditions, and. materials accordingto, this; invention; but it; is. tobe understood that: these: examples aresubmitted only by. way of illustration; and. not: limitatiom.

(A) Denmethomylation; of peel.

Five pounds of orange peel was ground? in a meat grinder; dispersed i'n-71'5 liters-of wate'r and sufficient 2- N sodiumhydroxide solution added to adjust the pH of themixture to 8.5". The temperature was maintained at about" 25" and the'pI-I maintained'at 8:5 for about l5 mihutes by gradual addition. of N sodium-hydroxide solution. This treatment had theefi'ect of par tially d'e-methox-ylatingthe pectinin; sit'uby. the actionor the :enzym espresent in the peel.

(B). ecidjle chinuoj, peel:

The. disp rsion was: thsnzrapidly acidified: to; ac pH of 2.0 by the addition of hydrochlorieaoidi'andi the temperature raised to 40 C. After a period of 30 minutes the dispersion was filtered. The filter cake was dispersed in 7.5 liters of water at 40 C. and the. pH adjusted to 2.0 by the addition of hydrochloric acid. After a period. of 30 minutes the dispersion was filtered. The filter cake was subjected to a third leaching as described above and the dispersion filtered. This treatment. results in the; removal of calcium from the peel and renders the. low-methoxyl pectinic acid therein capable of being extracted with water.

(C7 Extraction of Zow-methoryl pectinic acid Thev filter cake from the final leach was dispa sed in 6 liters of water and sufiicient sodium hydroxide added to establish a pH of 4.0. The dispersion was heated to boiling and at the end of, 30 minutes the dispersion was filtered with the aid of a. purified. diatomaceous earth filter aid. The filtrate was poured into 12 liters of 47.5% alcohol wh-ichhad been acidified to a pH of. 1.5. The pectinicacids which precipitated.werefilteredofi, washed with dilute alcohol and dried. A. yieldof (id-grams ot pectinic acid having a. methoxyl. content of. 4.1% was obtained.

In the-above exam-pie, the. filter aid was. purified by digesting itwi-tlr an. aqueous solution of. sodium. hexametaphosphate, the purpose. being. to remove. ironand other polyvalent metal ions.- which would tendto. form insoluble salts with. the pectinic acids. and thus. retain, them in the filter. cake- This: purification. can. also; be. accomplished by washing. the filteraidwith acid, followedby a-water wash- EXAMPLE 2" (A) De..-methoa:ylation of peel Twenty pounds of burred and sliced lemon peel; was suspended ingallons: of water- Forty-five grams; of sodium hydroxide was" added. to: bring: the pH to 8.7 in 10. minutes;. An additional 1'91- grams. of sodium hydroxide.- Was. added; over: aperiod of 23 minutes. Two: hundred ml. ofcon cent'rated hydrochloric acid was added to. reduce the pI-It0 2i0; Thedispersion wasra'pidly' heatedto:50.'C'. for afew'minutes, then thepe'elfiltered:

and placed in storage.

63) A'cidl leachin Fifteen; pounds; of; the stored peel. was; leached.

50 three times: using-: in; each;treatment, gallons of. water acidified with; hydrochloric acid to a. pH; of 2.0:and; operating at a. temperatureof 120 F:

(C) Extractionof low-methoryl pectz'm'cacid' Thepeelfrom the xfinalacid leach was-dispersed; in 50 lbs. of waterandthe pHadjusted to.4;3. by' addition of. sodium hydroxide. The dispersion washeatedto 20.091 and at. the end ofaeo-minute'z period. including; the time taken to raise: the. co temperatureto 93. C; (200 F.) ,the dispersiomwaszfiltered with: theeassistance of. a filter aid.-

(D7 Precipitationof" low-methowyl' pectinic acid To the filtrate was added 130 m1. concen-- 5 tratedsulphuricacid: and one gallon ofv alcohol.

The precipitate of low-methoxy-l pectinicacid." was. washed with dilute.- alcohol. and dried. The: low-methoxylx;pectinic. acid product had ameth oxyl content of 4.5%.. The yield: was about: 150 g,

As: set-.forth. abovethis: invention concernsxthez acid-leaching: vegetable material in which the pectin has; been: partially de methoxyl'ated im sitfui. suchzacidilea'ching has the primary effect of'removing: calciumdrom: the :vegetable material; is. and thus the low-methoxyl pectinic acids imthe:

peel can be extracted by water. The vegetable material may be partially de-methoxylated by a number of methods. Thus the partial de-methoxylation may be eiiected through hydrolysis by the use of acid, alkali, or enzymes.

As used herein, pectin is defined as the familiar preparation of commerce or the laboratory, prepared from plant extracts by precipitation with alcohol, acetone, or metallic salts with no attempt to modify its natural methoxyl content. By pectic acid is meant a completely de-methoxylated pectin, and by pectinic acid is meant any one of a series of derivatives of pectin with methoxyl content intermediate between that of pectin and pectic acid. Our process is particularly adapted to the isolation of low-methoxyl pectinic acids having a methoxyl content from about 2 to 5%.

Having described my invention, I claim:

1. The process which comprises leaching vegetable material, in which the pectin has been partially de-methoxylated in situ, with aqueous acid at a pH from about 0 to about 2.5, then extracting the low-methoxyl pectinic acids from the leached vegetable material by extraction with water adjusted to a pH from about 3.0 to about 5.0 by the addition of a base.

'2. The process which comprises leaching citrus peel, in which the pectin has been partially demethoxylated in situ, with aqueous acid at a pH from about 0 to about 2.5, then extracting the low-methoxyl pectinic acid from the leached peel by extraction with water adjusted to a pH from about 3.0 to about 5.0 by the addition of a base.

v3. The process which comprises leaching citrus peel, in which the pectin has been partially demethoxylated in situ, with aqueous acid at a pH from about 0 to about 2.5 until calcium is substantially completely removed from said :peel, then extracting the low-methoxyl pectinic acids from the leached peel by extraction with water adjusted to a pH from about 3.0 to about 5.0 by the addition of a base.

4. The process which comprises leaching citrus peel, in which the pectin has been partially demethoxylated in situ, with aqueous acid at a pH of about 2.0 until the calcium content of said peel is not greater than 0.2%, then extracting the low-methoxyl pectinic acids from the leached peel by extraction with water adjusted to a pH of about 4.0 by the addition of a base.

5. The process which comprises leaching citrus peel in which the pectin has been partially demethoxylated in situ, with aqueous hydrochloric acid at a pH of about 2.0 until the calcium content of said peel is not greater than about 0.2%, then extracting the low-methoxyl pectinic acids from the leached peel by extraction with water adjusted to a pH of about 4.0 by the addition of sodium hydroxide.

j 6. The process which comprises leaching vegetable material, in which the pectin has been partially de-methoxylated in situ, with aqueous acid at' a pH from about 0 to about 2.5.

'7. The process which comprises leaching citrus peel, in which the pectin has been partially demethoxylated in situ, with aqueous acid at a pH from about 0 to about 2.5.

8. The process which comprises leaching citrus peel, in which the pectin has been partially demethoxylated in situ, with aqueous acid at a pH from about 0 to about 2.5 until calcium is substantially completely removed from said peel.

9. The process which comprises leaching citrus .pe el, in which the pectin has been partially demethoxylated in situ, with aqueous acid at a pH 50f about 2.0 until the calcium content of said pen is not greater than 0.2%.

10. The process which comprises leaching citrus peel, in which the pectin has been partially demethoxylated in situ, with aqueous hydrochloric acid'at apH of about 2.0 until the calcium content of said :peel is not greater than 0.2%.

11. The process which comprises subjecting an aqueous dispersion of citrus peel to partial demethoxy1ation by enzymic hydrolysis, by adding an alkali to maintain the dispersion at a pH of 6 to 10, at a temperature of 0 C. to 60 C. for a period of no longer than about 30 minutes, acidifying to halt the hydrolysis, filtering off the peel,

situ in citrus peel to partial de-methoxylation,

leaching the citrus peel with aqueous hydrochloric acid at a pH of about 0 to about 2.5 at about 20 to 50 C. until the calcium content in the peel is about 0.2% or less, digesting the leached peel with hot water at a pH of about 3.0 to about 5.0, separating the peel from the Water, and recovering low-methoxyl pectinic acid from the water. HARRY S. OWENS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,444,266 Owens et al June 29, 1948 2,448,818 McCready et al Sept. 7, 1948 

6. THE PROCESS WHICH COMPRISES LEACHING BEGETABLE MATERIAL, IN WHICH THE PECTIN HAS BEEN PARTIALLY DE-METHOXYLATED IN SITU, WITH AQUEOUS ACID AT A PH FROM ABOUT 0 TO ABOUT 2.5. 